High efficiency airless spray tip design and use

ABSTRACT

A method of identifying a spray tip from a plurality of spray tips based on a selected fluid is presented. The method comprises the step of selecting the fluid. The fluid is characterized by a set of given physical parameters. The method also comprises the step of selecting an application pressure. The application pressure is sufficient to cause atomization of the fluid through the spray tip. The method also comprises the step of selecting the spray tip for the fluid applicator, based on characteristics of the fluid. The spray tip is selected based on an ability to process the fluid. The spray tip is selected such that the fluid has a viscosity on the order of 10 mPa·s in the shear rate range of 10 4 -10 6  s −1  to ensure a turbulent flow downstream of a pre-orifice.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on and claims the benefit of U.S.provisional patent application Ser. No. 62/442,565, filed Jan. 5, 2017,the content of which is hereby incorporated by reference in itsentirety.

BACKGROUND

Different fluids have different physical properties that dictateatomization rates, and atomization patterns. For the average consumerapplying a spray system, determining which conditions are necessary forachieving an even spray pattern can be difficult.

SUMMARY

A method of identifying a spray tip from a plurality of spray tips basedon a selected fluid is presented. The method comprises the step ofselecting the fluid. The fluid is characterized by a set of givenphysical parameters. The method also comprises the step of selecting anapplication pressure. The application pressure is sufficient to causeatomization of the fluid through the spray tip. The method alsocomprises the step of selecting the spray tip for the fluid applicator,based on characteristics of the fluid. The spray tip is selected basedon an ability to process the fluid. The spray tip is selected such thatthe fluid has a viscosity on the order of 10 mPa·s in the shear raterange of 10⁴-10⁶ s⁻¹ to ensure a turbulent flow downstream of apre-orifice.

The above summary is not intended to describe each illustratedembodiment or every implementation of the present disclosure

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings included in the present application are incorporated intoand form part of the specification. They illustrate embodiments of thepresent disclosure and, along with the description, serve to explain theprinciples of the disclosure. The drawings are only illustrative ofcertain embodiments and do not limit the disclosure.

FIGS. 1A and 1B illustrate a fluid spray applicator and system inaccordance with one embodiment of the present invention.

FIG. 2 is a flow diagram of a method of applying an even layer of fluidto a surface in accordance with one embodiment of the present invention.

FIG. 3 is a flow diagram of a method of designing a spray tip for agiven fluid in accordance with one embodiment of the present invention.

FIGS. 4-13 illustrate one example simulation for determiningcharacteristics of spray tips for different fluids.

While embodiments of the present invention are amenable to variousmodifications and alternative forms, specifics thereof have been shownby way of example in the drawings and will be described in detail. Itshould be understood, however, that the intention is not to limit theinvention to the particular embodiments described. On the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Different fluids have different physical parameters, e.g. viscosities.For example, within the paint family, different paints, primers,overcoats, etc. all have different properties. Additionally, differentfluids may have temperature-dependent or shear-rate-dependentviscosities. In order to achieve an even spray pattern of a fluid acrossa surface, it is necessary to atomize the fluid. Atomization can beachieved in various ways. One particular way is using an airless spraysystem. In such a system, it may be necessary to achieve a turbulentfluid flow upstream of the atomizing orifice, for example, by means of apre-orifice. Specific technological design and insights in fluiddynamics help to design spray systems and methods, such as thosedescribed herein, that provide improved spray pattern results.

As a result, different fluid applications may benefit from differentspray tip designs, for example because of differing viscosities,application temperature, etc. At least some embodiments described hereinallow for the design of a fluid spray tip based on known parameters of aparticular fluid application. Different spray tip designs may,therefore, result based on the fluid to be applied. For example, atleast some of the spray tip designs described in U.S. Patent ApplicationPublication No. 2016/0303585 A1, published Oct. 20, 2016, which ishereby incorporated in its entirety, are designed for better applicationresults with some fluids as compared to others.

FIGS. 1A and 1B illustrate a fluid spray applicator and system inaccordance with one embodiment of the present invention. FIG. 1Aillustrates a spray gun 10, for example, for use in a paint sprayingsystem. Paint, or another exemplary fluid, enters through spray guninlet 20, and exits from spray gun outlet 50, after passing through afluid channel (not shown) within spray gun 10. In one embodiment, aspray tip (not shown) is attached to outlet 50 to produce a desiredspray pattern. The spray tip may include a spray tip pre-orifice designdesigned based on known fluid and application properties, as describedin greater detail below. Spray tips may be built into spray gun 10, asinternal components. Alternatively, spray gun 10 may be configured tointerchangeably receive different spray tips, with different pre-orificedesigns, each design configured to provide excellent performance basedon anticipated properties of a fluid to be sprayed, and/or applicationconditions. Spray tips may be selected such that, at outlet 50,turbulent fluid flow of a fluid is increased.

FIG. 1B illustrates a fluid spray system 100, specifically an airlesssystem, in accordance with one embodiment of the present invention.Fluid spray system 100 illustratively retrieves fluid from a fluidsource 110 for application on a target surface 160. Fluid source 100 mayinclude a fluid with one or more fluid parameters 112. For example,density, viscosity, etc. Further, each of such parameters may vary withtemperature and/or humidity.

Fluid from fluid source 110 is provided to a pump 120, where the fluidis pressurized. Fluid may be pressurized to an application pressure, forexample. Alternatively, fluid may be over-pressurized by pump 120 inorder to compensate for pressure losses associated with thetransportation mechanism between pump 120 and applicator 140. In someembodiments, the pressure of fluid exiting pump 120 is set manually by auser. For example, low pressure systems may include an applicationpressure below 3000 PSI.

Fluid spray system 100 also includes a heater 130 to heat the fluid to agiven temperature prior to application. Heating a fluid to a desiredapplication temperature may be helpful in order to ensure consistentapplication patterns from use to use. For example, some paints havetemperature dependent viscosity, and therefore may behave differentlywhen applied by a user in a cold vs. a warm application condition.Therefore, heating the fluid to a consistent temperature, and sprayingthe fluid at a fixed temperature, may help to reduce deviations in spraypatterns from use to use. However, it is expressly contemplated thatembodiments may be practiced that omit a heater, for example if a fluidapplication is to occur at ambient temperatures. In such a scenario,pump 120 may deliver fluid directly to applicator 140.

Fluid spray system 100 also includes an applicator 140. Applicator 140may include a spray tip 150, which may have one or more spray tipparameters 152. Spray tip parameters 152 can include, for example,material composition as well as internal geometric design. Internalgeometries of different spray tips 150 may allow for better performancewith one fluid over another, based on the fluid parameters 112. Spraytip 150 may be designed, for example based on fluid parameters 112, toensure sufficient turbulence of a fluid prior to delivery fromapplicator 140 to target surface 160.

For example, a spray tip 150 may include a turbulating chamber, anexpansion chamber, a contraction chamber, or a plurality of suchchambers in succession. The spray tip parameters 152 may be selected orotherwise determined based on anticipated use with a specific fluid, forexample such that the desired fluid achieves a desired level ofturbulence prior to application on target surface 160. For example, auser of a fluid spray system 100 may obtain a kit of interchangeablespray tips 150 such that tips can be used for different fluids. The useof optimized, or spray tips specifically designed for different fluidsmay help to ensure that a user achieves a desired fluid spray pattern.

A successful fluid spray system design requires consideration of severalelements, including the spray tip, the fluid rheology of the fluid beingapplied to surface 160, and rheology modification options. The fluidshould have a rheology consistent with application at low pressures,specifically a sufficient viscosity in a desired shear rate range.Rheology modification mechanisms, such as heating, can be helpful totune fluid rheology for a given application. Shear-thinning behavior fora paint can be improved, in one embodiment, through the use ofmodifiers, or additives. Increased shear-thinning behavior may produceimproved spray patterns. For example, the ACRYSOL™ line of modifiers,provided by DOW® (Dow Chemical Company with headquarters in Midland,Mich.) that increases shear-thinning, and can produce a pseudoplasticrheology profile. A pseudoplastic fluid is a non-Newtonian fluid thatloses viscosity when shear rate increases, but recovers viscosity whenthe shear rate decreases.

One potential additive is the DOW-ACRYSOL-ASE modifier. ASE thickenerstend to be high in molecular weight, which allows for efficientthickening. Another potential additive is the DOW-ACRYSOL-ASE-60-ER,which is a highly shear-thinning rheology modifier that providesresistance to sedimentation and sagging. The DOW-ACRYSOL-HASE modifieris another efficient and strong shear-thinning modifier. Additionally,other modifiers are also available.

At least some of the systems and methods described herein may be usefulwith one or more spray tips described and illustrated in U.S. PatentApplication Publication No. 2016/0303585.

FIG. 2 illustrates a method of applying an even layer of fluid to asurface in accordance with one embodiment of the present invention.Method 200 may be used, with fluid spray system 100, for example, inorder to apply a fluid from a fluid source 100 to a target surface 160(shown in FIG. 1B). However, while method 200 is described in thecontext of spray system 100, it can also be implemented within otherappropriate systems. Spray tip 150 may be selected, for example, basedon fluid characteristics of the fluid to be applied, as well as theapplication parameters—e.g. temperature, humidity, etc.

At block 210, an application spray tip is selected and attached to anapplicator. For example, spray tip 150 may be selected based on one ormore fluid characteristics, as indicated in block 202. Additionally,spray tip 150 may be selected based on tip parameters 152 which mayachieve desired atomization characteristics for a fluid, as indicated inblock 204. Additionally, spray tip 150 may be selected to increaseperformance of a particular fluid based on known shear thinning behavior(for example, to achieve a particular shear rate) of the particularfluid, as indicated in block 206. Additionally, other fluidcharacteristics may influence the selection of a spray tip for a givenapplication as indicated in block 208. In one embodiment, selecting anapplication spray tip includes selecting one spray tip out of a kit ofspray tips, each spray tip in the kit being configured for use indifferent application scenarios.

In block 220, an application pressure is set. Application pressure maybe set based on fluid characteristics, as indicated in block 212.Additionally, application pressure may be selected to achieve desiredatomization characteristics, as indicated in block 214. For example, afluid may need to be sprayed at a sufficiently high pressure to fullyatomize the dispensed fluid. However, lower pressures may also bedesired. For example, low pressures, approximately 1,000 PSI or lower,may be desired. Additionally, the application pressure may be selectedto ensure a sufficient flow rate is achieved to produce turbulence in atip of a particular design, accounting for the specific shear thinningbehavior of a fluid, as indicated in block 216. Additionally, however,pressure may be bounded by other constraints, as indicated in block 218.

In block 230, an application temperature is set. For example, differentfluids may have temperature-dependent viscosities, such that it isnecessary to heat up a fluid to a desired temperature to achieveconsistent and even application of fluid. For example, in oneembodiment, fluid is heated to a desired temperature and sprayed at thatfixed temperature during the entirety of an operation. The applicationpressure may be set based on fluid characteristics, in one embodiment,as indicated in block 222. In another embodiment, applicationtemperature may be set by atomization characteristics of a fluid, asindicated in block 224. Additionally, in another embodiment, applicationtemperature selected to ensure the fluid viscosity falls within adesirable range, accounting for the shear and temperature dependencies,as indicated in block 226. However, other constraints may dictate whichtemperature a fluid is applied to a surface for a given application, asindicated in block 228.

In block 240, fluid is applied evenly to a surface. For example, a userengages the trigger of an applicator, such as applicator 140, allowingfluid to flow through the applicator, interact with the internal flowpath of spray tip 150, and onto a target surface 160.

FIG. 3 illustrates a method of designing a spray tip for a given fluidin accordance with one embodiment of the present invention. Method 300may be useful, for example, given a fluid with known properties and flowcharacteristics. Different fluids have different properties, andtherefore it is necessary that spray tips be designed to accommodatedifferent characteristics of different fluids. For example, differentfluids require different geometries within a spray tip to achieve thedesired amount of turbulence prior to an application. Some examples ofspray tip geometries are described in U.S. Patent ApplicationPublication 2016/0303585 A1.

Method 300 may be useful to design a spray tip, such as spray tip 150illustrated in FIG. 1, for example, with specific tip parameters 152 fora specific fluid source 110. In at least one embodiment, spray tip 150is designed with different tip parameters 152 to accommodate a specificfluid, such that a spray tip A is more advantageously used with a fluidA than a spray tip B, while spray tip B may be more advantageously usedfor a fluid B than spray tip A.

In block 310, fluid rheology is determined. For example, differentfluids have different Reynolds numbers under different conditions, as afunction of fluid properties and operating conditions. In oneembodiment, determining a fluid rheology includes determining Reynoldsnumbers for the fluid under different conditions, as indicated in block302. Additionally, determining fluid rheology may include determiningatomization characteristics for the given fluid, as indicated in block304. Other fluid rheology features may also be necessary to determine,as indicated in block 306. For example, a fluid's viscosity with respectto different temperatures may be helpful, to determine both a desiredspray tip configuration, and a desired application temperature.Additionally, fluid characteristics, for example viscosity, at differentshear rates may be necessary to design a spray tip for a fluid for agiven set of application parameters.

In block 320, flow parameters are tuned for a given fluid. For example,some flow parameters for a fluid can be adjusted. Tuning a viscosity ofa fluid, as illustrated in block 314, for example, may include selectingan appropriate temperature for application of the fluid so that adesired viscosity is achieved for an application. Additionally,turbulence features may be tuned for a given fluid, as indicated inblock 316. Turbulence features may include determining appropriateinternal geometries to include expansion and contraction chambers that afluid flows through within a spray tip. Additionally, pressure may betuned for a given fluid, as indicated in block 318.

In block 330, the spray tip is designed with characteristics appropriatefor the fluid rheology, particularly considering the fluid's shearthinning behavior. For example, a series of pre-orifice chambers may besized to achieve turbulent flow for a fluid with a properly designedshear thinning behavior. For example, a total length of the spray tipmay be increased or decreased, with respect to a standard spray tip.Additionally, a diameter of an internal chamber may change, or a rate ofexpansion/contraction may be altered in order to achieve a desiredturbulence.

According to another aspect of the invention, a fluid rheology isdetermined by aspects of physical parameters of a fluid being applied.As mentioned, different fluids have different Reynolds numbers underdifferent conditions, and exhibit different fluid properties underdifferent fluid conditions. Adjusting viscosity of a fluid can beachieved in many ways, e.g. by adjusting a given mixture of fillers,polymers and dispersion particles. In one embodiment, adjusting a fluidrheology includes adjusting Reynolds numbers for a fluid under differentconditions or recipes. Additionally, adjusting a fluid rheology mayinclude adjusting atomization characteristics for the given fluid. Otherfluid rheology features may also be adjustable. For example, a fluid'sviscosity with respect to different temperatures may be determinedempirically or via simulation data such that an application temperaturecan be selected. Determined parameters can be used for a desired spraytip, and a desired application temperature. Additionally, fluidcharacteristics at different pressures may be influenced by shearthinning parameters that are tuned for an application fluid. Forexample, a shear rate may be tuned for a given fluid by adjustingpolymer dispersion parameters. Additionally, turbulence features may betuned for a fluid by adjusting dispersion rates, filler particles,polymer properties or other ingredients of the fluid. Turbulencefeatures may be suggested by appropriate geometries for expansion andcontraction sections of a spray tip.

FIGS. 4-14 illustrate one example simulation for determiningcharacteristics of spray tips for different fluids. A simulation may beuseful, for example in conjunction with method 300 to determineappropriate spray tip geometry and operating constraints for a givenfluid. Additionally, given pressures and internal spray tip geometriescan be simulated in order to receive physical parameters of a fluid tobe processed at an improved atomization result and desired spraypattern. The example presented in FIGS. 4-14 is provided forillustration purposes only and should not be considered to limit anyaspect of the invention or any systems and methods described herein.

Simulations were performed to determine shear rates and strain ratesexperienced by fluid flowing through two different spray tips. The firstspray tip is spray tip A, identified under the trade designation of NGA519. The second spray tip, spray tip B, identified under the tradedesignation NESPRI®. For both styles of spray tips, water and NESPRI®paint were sprayed at a pressure of 1450 PSI. Characteristics for theNESPRI® paint are described in U.S. Patent Application Publication No.2007/129469. The Wagner NGA tip was designed to have a turbulent inletcondition with respect to the atomizing orifice, which is not present inthe tip designed for use with the paint described in the '469 patentapplication publication (hereinafter referred to as the '469 tip and'469 paint respectively), which does not have a pre-orifice. From theperspective of paint rheology, the NGA tip requires the transition toturbulence by means of a pre-orifice, whereas the '469 tip onlytransitions after the pre-orifice. Each of the tips used in thepresented example include a cat eye atomizing orifice. Upstreamturbulence allows the NGA tip to spray at pressures of 1000 PSI orlower, a condition desirable for many paint sprayer for, for example,efficiency, material savings, and overspray reduction.

FIG. 4 illustrates the results 400 of a simulated flow of the '469 paintthrough the NGA519 tip. The results of the simulation suggested that thedominant shear rate regime in the NGA519 tip is 10⁴-10⁶ s⁻¹. There are,of course, regions with lower shear, and regions with much greater shear(very near the surface, for example). The shear rate range of 10⁴-10⁶s⁻¹ is what a considerable amount of the fluid in the boundary layer andthe turbulent jet exiting the pre-orifice experiences. This is also thecharacteristic strain rate regime. This range was then identified to beappropriate for both water and the '469 paint, and is thereforeconsidered to be dominantly controlled by the volumetric flow rate ofmaterial and the length scale of the tip. For proper operation of thepre-orifice, it is therefore favorable for a paint to have a viscositythat results in a local Reynolds number near 1500 when the shear rate isin the range of 10⁴-10⁶ s⁻¹. Therefore, it is favorable for the dynamicviscosity of paint to be on the order of 10 mPa° s in the shear raterange of 10⁴-10⁶ s⁻¹. This will promote turbulent flow in the NGApre-orifice, which allows for spraying at reduced pressures. This isalso expected to improve low pressure atomization in the '469 tip.

Currently, '469 paint, according to laboratory measurement, has aviscosity about one order of magnitude greater than the desired value inthe critical shear rate range. This results in a laminar flow downstreamof the pre-orifice in the NGA 519 tip, as shown in results 400. Thislaminar flow is demonstrated in FIG. 4, which presents the time averagestrain rate within the NGA tip. The lighter regions highlight thelaminar boundary layer (the strain rate being in the range of 10⁴-10⁶s⁻¹, except at the solid surface where the strain rate is much greater).This laminar flow contrasts with the turbulent flow that occurs whenspraying water.

Results 500 of a simulation of water sprayed through the NGA 519 tip areillustrated in FIG. 5. For water, the clear edges of the boundary layerare not observed because the pre-orifice has produced a turbulent flow.The influence of the turbulence is observed near the cat eye orifice,where there is a non-zero strain rate throughout the fluid crosssection.

The difference in performance between laminar and turbulent flow canalso be observed through volumetric histograms of strain rate 600 and700, which appear in FIG. 6 for the '469 paint, and FIG. 7 for water,respectively. For the '469 paint, all realized strain rates resulted inthe dissipation of turbulent energy. The total volume of paint thatexperiences a given strain rate is therefore monotonically decreasingwith strain rate. For water, however, a spike in volumetric density isobserved centered around 10⁵ s⁻¹. This peak occurs because the viscosityof water is low enough in the proper strain rate range to produceturbulence, which introduces additional volumetric concentration in thecorresponding turbulent length scales.

The NGA 519 tip will not spray '469 paint particularly well at the givenoperating point. This is because the '469 paint viscosity in thecritical shear rate range of 10⁴-10⁶ s⁻¹ is too large to produce aturbulent flow.

With this information in mind, it is possible to better design therheology of '469 paint. Two things are required: high viscosity at lowshear rates to make certain the paint does not run while drying on awall or when applied to a brush/roller, and a viscosity on the order of10 mPa° s in the shear rate range of 10⁴-10⁶ s⁻¹. These two parametersshould ensure turbulent flow and therefore favorable spray performance,and can be achieved by modifying the power law expression generatedexperimentally for '469 paint.

A viscosity expression was required to run the simulations of water and'469 paint. In order to produce the expression, a curve was fit toexperimentally measured viscosity as a function of shear rate, which ispresented as results 800 in FIG. 8. The two experimental trials thatwere run have different power law relationships. Trial 2 was selectedfor having shear rate more appropriate for airless spraying. To producea paint that is more favorable for airless spraying, the magnitude ofthe exponential must be increased. In other words, the shear thinningbehavior of the paint needs to be amplified. The exponential termproduced by curve fitting the experimental data has a value of −0.261.Trial 1, illustrated by reference number 810, had a curve fitting ofy=30088x^(0.599), with an R² value of 0.9912. Trial 2, represented byreference numeral 820, had a curve fitting of y=3690.8x^(0.261), with anR² value of 0.9828.

As illustrated in FIG. 9, the '469 façade value, represented byreference numeral 910, was modified to −0.35 and −0.45, illustrated aspower law 1 and power law 2, represented by reference numbers 920 and930, respectively. Both modified forms illustrate high viscosity at lowshear rates, which ensures that paint, once sprayed, will stick firmlyto a wall/roller/brush. Both modified forms are also presented with theresults of a water sample 940.

Simulations of the current '469 paint resulted in a laminar flow, whilesimulations of both modified '469 fluids results in turbulent flows.Histograms of the volumetric distribution of strain rates for the twomodified fluids appear in FIGS. 10A and 11A as rate distributions 1000and 1100, respectively. The corresponding strain rate contours for thefluids are illustrated in FIGS. 10B and 11B, as contours 1050 and 1150,respectively. Both cases have the characteristic distribution ofturbulent length scales just below 10⁵ s⁻¹. The case with an exponentialof −0.35 illustrates a more viscous flow, and therefore has a lessdistinct peak with an onset of dissipation at a lower strain rate. Thisresult supports the hypothesis that increasing the shear thinningbehavior of the paint has the potential to improve spray performance forthe NGA tip. Because the viscosity at low shear rates is effectivelyunchanged from the current '469 paint, the modification should notimpact performance for rolling or brushing.

The '469 tip, illustrated in FIGS. 12 and 13 as contours 1200 and 1300,respectively, was also considered to potentially modify the paintrheology to improve atomization behavior. It is known that less viscousfluids are more easily atomized, which suggests that the improvementsdiscussed above for the NGA519 tip may also improve performance for the'469 tip.

FIG. 12 illustrates a cross-section 1200 of one '469 tip spraying waterat 1450 PSI. The contour shown in the strain rate. Similar to the NGA519 tip, the prominence of strain near 10⁻-10⁶ s⁻¹ is observed. Thisstrain rate is preserved just downstream of the cat eye orifice, whichis the region where primary atomization will occur, and where largescale topological features of the spray pattern will be determined(lines, tails, pattern shape, etc.). It is therefore favorable for paintto have a reduced viscosity in this strain rate neighborhood.

FIG. 13 illustrates the results when using '469 paint. Again, theprominence of strain of the same magnitude is observed, but a muchthicker boundary layer is also observed. The thicker boundary layer iscaused by the higher viscosity of the '469 paint when compared to water.However, downstream of the cat eye orifice, the strain rate appears verysimilar to the water case.

It is expected that the results would be qualitatively the same for highpressure spray tips as those shown with the '469 spray tip describedherein. However, a slight upscaling of the strain rates would beexpected, the wall strain rate would be greater, and strain rates in theboundary layer would also be greater. The important strain range wouldfall within 10⁴-10⁶ s⁻¹, as only an approximate 20% increase in materialflow for the same size tip would occur.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. Additionally, while one example has beenpresented with respect to two different types of paint, it is also to beunderstood that similar methods can be applied for other fluidapplications, including other types of paints, primers, coatings, etc.

What is claimed is:
 1. A spray system comprising: a fluid applicator; afluid pump that pumps a fluid from a fluid source to the fluidapplicator, wherein the fluid pump operates at a pressure at or below2,000 PSI; an airless spray tip configured to couple to the fluidapplicator and atomize the fluid, the airless spray tip comprising: aninlet; an outlet; a flow path extending between the inlet and theoutlet, the flow path comprising an internal geometry, comprising,sequentially in an upstream to downstream order: a first cylinder; afirst expanding section that comprises a widening frustoconical surfacethat widens in a downstream direction; a second cylinder that has adiameter that is larger than a diameter of the first cylinder; a thirdcylinder that has a diameter that is larger than the diameter of thesecond cylinder and wherein the diameter of the third cylinder is largerthan a length of the third cylinder; a first contracting section thatcomprises a narrowing frustoconical surface that narrows in thedownstream direction; and a fourth cylinder that has a diameter that issmaller than the diameter of the second cylinder and the diameter of thethird cylinder; and wherein the internal geometry is sized such that thefluid has a viscosity on the order of 10 mPa·s in a shear rate range of10⁴-10⁶ s⁻¹ upstream of the outlet.
 2. The spray system of claim 1,further comprising a heater that elevates the fluid to an applicationtemperature selected to achieve the viscosity of the fluid in the spraytip.
 3. The spray system of claim 1, wherein the pump operates at aspray pressure at or below 1,000 PSI.
 4. The spray system of claim 1,wherein the internal geometry is configured to reduce overspray of thefluid from the fluid applicator.
 5. The spray system of claim 1, whereinthe first expanding section is longer in an upstream to downstreamdirection than the first cylinder.
 6. The spray system of claim 1,wherein the first contracting section is shorter in an upstream todownstream direction than the first expanding section.